<!DOCTYPE html>
<html lang="en" style="height: 100%">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body style=" height: 100%;">

<div style="width: 100%;height: 100%; display: flex;justify-content: center; align-items: center; text-align: center">

    <table>
        <form action="/test/t1" method="post">
            <tr>
                <td colspan="3">
                    <input type="text" id="v1" name="v1" value="1" readonly/>
                </td>
            </tr>
            <tr>
                <td>
                    <input type="button" value="1" onclick=" document.getElementById('v1').value = 1 "/>
                </td>
                <td>
                    <input type="button" value="2" onclick=" document.getElementById('v1').value = 2 "/>
                </td>
                <td>
                    <input type="button" value="3" onclick=" document.getElementById('v1').value = 3 "/>
                </td>
            </tr>
            <tr>
                <td>
                    <input type="button" value="4" onclick=" document.getElementById('v1').value = 4 "/>
                </td>
                <td>
                    <input type="button" value="5" onclick=" document.getElementById('v1').value = 5 "/>
                </td>
                <td>
                    <input type="button" value="6" onclick=" document.getElementById('v1').value = 6 "/>
                </td>
            </tr>
            <tr>
                <td>
                    <input type="button" value="7" onclick=" document.getElementById('v1').value = 7 "/>
                </td>
                <td>
                    <input type="button" value="8" onclick=" document.getElementById('v1').value = 8 "/>
                </td>
                <td>
                    <input type="button" value="9" onclick=" document.getElementById('v1').value = 9 "/>
                </td>
            </tr>
            <tr>
                <td colspan="3"><input type="submit" value="submit"/></td>
            </tr>
        </form>
    </table>


</div>
</body>
</html>

<style>
    input {
        width: 100px;
        text-align: center;
    }
</style>